1. Field of the Invention
The present invention relates to a sensor, and more particularly, to a sensor such as a gas sensor (e.g., an oxygen sensor, an NOx sensor, or an HC sensor) for detecting the concentration of a specific gas component in exhaust gas exhausted from, for example, an internal combustion engine, or a temperature sensor for detecting the temperature of the exhaust gas.
2. Description of the Related Art
Conventionally, a gas sensor has been used for air-fuel-ratio control of an automobile. Such a gas sensor includes a sensor element whose electrical characteristics change in accordance with the concentration of a specific gas component within exhaust gas (Patent Document 1). FIG. 12 shows such a gas sensor (hereinafter also referred to as a “sensor”) 1. This gas sensor 1 includes a sensor element (hereinafter also referred to as an “element”) 21 formed of a solid electrolyte having oxygen-ion conductivity; a metallic shell body 11 for holding the sensor element 21; a metallic protection sleeve 81 provided at a rear end (an upper end in FIG. 12) of the metallic shell body 11; metallic terminal members 51 electrically connected to electrode terminals 25 provided on side surfaces 24 of a rear end portion of the sensor element 21; lead wires 61 connected to the metallic terminal members 51 and extended outward from the rear end of the protection sleeve 81; a separator 71 disposed within the protection sleeve 81 so as to insulate the plurality of metallic terminal members 51 and the lead wires 61 connected thereto; an elastic seal member 101 through which the lead wires 61 are extended to the outside of the protection sleeve 81 and which seals the protection sleeve 81; etc. Notably, in the present specification, when the term “rear end” is used for the sensor 1, its component, or a section (portion) thereof, it refers to an upper end of the sensor, component, or the like in FIG. 12. Also, when the term “front end” is used for the sensor 1, its component, or a section (portion) thereof, it refers to a lower end of the sensor, component, or the like in FIG. 12.
In the sensor 1 having the above-described structure, the separator 71 is formed of an electrically insulative material such as ceramic, and includes terminal spaces 75 formed therein such that the spaces 75 penetrate the separator 71 in the front-rear direction, as shown in FIGS. 12 and 13. The metallic terminal members 51 are positioned and accommodated within the respective spaces 75, so as to insulate the metallic terminal members 51 and the lead wires 61. The respective metallic terminal members 51 are formed from a metal plate by pressing and bending operations. A plate spring portion 53 is provided at the front end of each of the metallic terminal members 51, and is resiliently pressed against the corresponding electrode terminal 25 provided on the side surface 24 of the sensor element 21 by means of the plate spring portion 53. In this manner, the metallic terminal member 51 is electrically connected to the electrode terminal 25. Further, the metallic terminal members 51 each has a crimp portion 57 formed at the rear end thereof such that the crimp portion 57 connects to the plate spring portion 53 via a junction line portion 55. By crimping the crimp portion 57, the metallic terminal member 51 is connected to the conductor of a corresponding lead wire 61. The lead wires 61 are passed through lead-wire passage through holes 105 formed in the elastic seal member 101 such that the holes penetrate in the front-rear direction, and are extended to the outside.
In the conventional sensor 1 having the above-described structure, the sensor element 21 assumes the form of an elongated plate. As shown in FIG. 12, for example, three electrode terminals 25 are laterally arranged on one side surface 24 of the rear end portion of the sensor element 21. Similarly, for example, two electrode terminals 25 are laterally arranged on the other side surface 24 of the sensor element 21 at the rear end thereof. Meanwhile, the metallic terminal members 51 are disposed so as to be laterally arranged in the terminal spaces 75 of the separator 71, and, as described above, the plate spring portions 53 are electrically connected to corresponding electrode terminals 25 within the terminal spaces 75. In this sensor 1, the conductors of the lead wires 61 are connected to the crimp portions 57 of the corresponding metallic terminal members 51 by bending crimping fingers 58 of the crimp portions 57 toward the side where the electrode terminals 25 of the sensor element 21 are present (on the side where an axis G is present in FIG. 12).    [Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 2007-47093
3. Problems to be Solved by the Invention
Incidentally, in the sensor 1 having the above-described structure, the elastic seal member 101 is compressed in the radial direction when a smaller-diameter portion 83 at the rear end of the protection sleeve 81 is circumferentially crimped in a state in which the lead wires 61 are passed through the through holes 105. As a result, sealing is established at, among other locations, the through holes 105 through which the lead wires 61 are passed. In such a structure, from the viewpoint of sealing performance, the lead wires 61 passing through the through holes 105 are preferably compressed as uniformly and efficiently as possible. For such uniform and efficient compression, the through holes 105 are desirably disposed as follows. Since in general the elastic seal member 101 has a roughly circular transverse cross section (a shape as viewed in the front-rear direction of the sensor 1) as shown in FIG. 14, the through holes 105 are desirably disposed along a circle (imaginary circle) concentric with the transverse cross section at equal angular intervals or intervals similar thereto such that the through holes 105 are located as close as possible to the outer circumferential edge of the transverse cross section. Therefore, in the sensor 1 of FIG. 12, a through hole (hereinafter also referred to as the “center through hole”) 105, which is one of the through holes 105 corresponding to one side surface 24 carrying the laterally arranged three electrode terminals 25 and through which the lead wire 61 connected to the center metallic terminal member is passed, is desirably provided such that the center through hole 105 is located outward in relation to through holes (hereinafter also referred to as the “side through holes”) 105 through which the lead wires 61 connected to the side metallic terminal members located at opposite lateral ends are passed, as viewed from the rear side.
However, the metallic terminal members 51 connected to the electrode terminals 25 of the sensor element 21 in the above-described manner are disposed within the terminal spaces 75 of the separator 71 such that the metallic terminal members 51 are laterally arranged to face the electrode terminals 25 (see FIG. 13). Therefore, under the assumption that the entirety of each metallic terminal member 51, excluding the plate spring portion 53, is approximately straight, the crimp portions 57 of the metallic terminal members 51 are also laterally arranged. Accordingly, for example, measures as described below must be taken in order to enable the lead wire 61 connected to the center metallic terminal member 51 to be passed through the center through hole 105 of the elastic seal member 101 and extended to the outside.
According to one measure, the crimp portion 57 of the center metallic terminal member 51 is separated from the corresponding electrode terminal 25 of the sensor element 21 as viewed from the rear side. That is, the junction line portion 55 between the plate spring portion 53 and the crimp portion 57 is bent into, for example, a crank shape, so as to separate the crimp portion 57 from the corresponding electrode terminal 25. According to another measure, a clearance is formed along the front-rear direction between the separator 71 and the elastic seal member 101 without deforming the metallic terminal members 51, and a front end of the lead wire 61 connected to the crimp portion 57 of the center terminal electrode 51 is bent into a crank shape.
However, the measure of bending the metallic terminal member 51 or the front end of the lead wire 61 within the small sensor 1 is not so easily accomplished, and an increase in the size of the sensor is unavoidable. That is, in order to allow for such bending, the size of the separator 71 must be increased, or a large space within the sensor which extends in the direction of the axis G (the front-rear direction) must be secured. For example, in the case where a metallic terminal member 51 whose junction line portion 55 is bent is accommodated within the corresponding terminal space 75 of the separator 71, the length and cross-sectional area of the space 75 must be increased. Further, in the case where the lead wire 61 is bent, a clearance must be formed along the front-rear direction between the separator 71 and the elastic seal member 101 with a resultant increase in the size of the sensor.